1. Field of the invention
The present invention relates to composite materials and particularly to the fabrication of articles from laminates wherein each layer is a composite consisting of uniformly distributed fibers captured in a matrix material. More specifically, this invention is directed to techniques for the manipulation of mono and multilayer composite tapes, which tapes include a resinous matrix material in the uncured state, to achieve the stacking of such composite tapes as a step in the fabrication of usable structures therefrom. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the prior art
A novel method for the handling of pre-impregnated composite tapes is disclosed in copending U.S. Patent application Ser. No. 573,040 of E. R. More and H. A. Nutter, Jr. filed Apr. 30, 1975 and assigned to the assignee of the present invention. The disclosure of application Ser. No. 573,040 is incorporated into the disclosure of the present application by reference.
To briefly summarize the method of application Ser. No. 573,040, the composite in sheet or tape form, with the resinous matrix material in an uncured state, is sandwiched between liners and positioned on a cutting table. A numerical tape controlled reciprocating cutter thereafter generates the desired ply shapes; the layers of the desired end product thus being formed in place and in accordance with a predetermined distribution pattern. Subsequent to ply generation, the upper liner is stripped from the composite material to expose the tacky upper surface of the composite material. Thereafter a ply stacking operation is performed. During the course of this ply stacking operation an automatic stacking heat is employed to pick up and compact the plies in sequence with each subsequently picked up piece of pre-impregnated composite tape being oriented such that pieces are in their designated and required location relative to one another. During the stacking procedure, which deposits the plies on the pick-up head, the adhesive tack of the exposed upper ply surfaces is utilized to achieve ply-to-ply adherence and the lower liner will remain on the cutting table since the adhesive attraction between plies of the composite is greater than that between the composite and lower liner while the holding force, usually a vacuum, between the lower liner and the table is greater than the adhesive attraction of the lower liner to the resin. After stacking has been completed the precision stacked plies are removed from the pick-up head for final compaction and curing.
The initially utilized stacking head employed a foot which descended over the selected ply and lifted it vertically from the table surface. As a result of the high relative bond strength between the composite and lower liner, unsatisfactory results have often been achieved using a direct vertical lift.